Maybe Oenothera filiformis.

http://michiganflora.net/image.aspx?img=8877&id=1760

http://phytoimages.siu.edu/users/paraman1/9_4_14/upload4Sept14a/OenotheraFiliformis02.jpg

I was thinking Oenothera also and that one looks like it.

Your plant is pretty tall and sparsely branched for Oenothera filiformis (previously Gaura longiflora). I wonder if it is the similar, but somewhat larger Oenothera demareei (previously Gaura demareei). They're pretty easy to tell apart. O. filiformis has flowers about 3/4 inch across that open near sunset, and is pollinated by moths. O. demareei has flowers about 1 inch across that open in the early morning hours, and is pollinated by bees. If it is Gaura demareei, that one is a native, with its primary range in Arkansas.

It does look more like Oenothera filiformis than the other bee-blossoms; if so, I wonder how it got to my yard in SC? I kept looking at the Oenothera/Gaura species that should be in my area, and they don't quite look right either.

I was somewhat reassured, though, to read this statement at the Lady Bird Johnson Wildflower site: "The genus is easily recognized, but the species are sometimes difficult, due partly to a great deal of hybridization."

I had trouble finding info about the usual height of these various species. Also, some seem to have leaves all along the stalk, while my plant has leaves at the bottom, then a stalk that is free of leaves, but plenty of those odd-looking buds and flowers.

Sometimes I am pretty slow on the uptake... I did not realize until I read a blurb at the Smithsonian web site that these things bloom at dusk. So I was discounting images with fully opened flowers because I hadn't looked at this plant with the flowers fully open. Duh! Looks different by flashlight...

So I guess I'll go with O. filiformis or a hybrid with no "upper foliage".

Thanks,

Virginia

gardengal, I can see why you might think of cleomes, but the foliage is quite different. I actually have a cleome (not one of the native species) right near this other plant, and the cleome is shorter, and has compound leaves.

jekeesl, the plant has branched out more with maturity, as compared with the second photo I posted above which dates from at least a month ago. O. filiformis does seem more well-branched than my plant. However, I did just go out with a flashlight and the blooms are open and covered with much pollen, so I'd guess moth pollination.

I haven't seen any photos that look exactly like my plant, and neither of the species named are native to South Carolina. I do have a friend in TX who has sometimes shared plants with me, so if it is O. filiformis or O. demareei, I'd have to assume that's how it got here. I do wonder if it might be a hybrid, though.

Virginia

You mentioned a comment from the Lady Bird Johnson Wildflower site: "The genus is easily recognized, but the species are sometimes difficult, due partly to a great deal of hybridization.". We have large, mixed populations of both filiformis and demareei in this part of Arkansas, but no known hybrids of the two. So I checked USDA, and they have zero listings for Oenothera hybrids. But, I did find greenhouse cultivars of O. filiformis offered online. In any case, Oenothera filiformis is variable in branching, so shifts in general form are normal for the species. Finally, your comment about the pollen is spot on. If you see flowers that are open just after sunrise, it isn't always obvious if those are waning filiformis, or freshly-opened demareei. But ... if the open flowers have fresh pollen, that clearly defines the flowering event and species. Your plants are typical for O. filiformis.